How do I clean my furnace flame sensor?

Cleaning your furnace flame sensor is a simple maintenance task that can solve ignition problems, but safety precautions are essential when working around gas appliances.

The flame sensor is a small metal rod (usually about 4-6 inches long) located near the burner assembly that detects whether the gas is actually burning. When it gets dirty or corroded, it can't properly sense the flame, causing your furnace to shut down for safety. Before starting any work, turn off power to your furnace at the electrical panel and turn the gas valve to "OFF."

To clean the sensor, you'll need to remove the furnace access panel and locate the flame sensor rod near the burners. Carefully disconnect the wire connector and remove the mounting screw to pull out the sensor. Use fine-grit sandpaper (220-grit) or steel wool to gently clean the metal rod until it's shiny. Avoid using harsh chemicals or coarse abrasives that could damage the sensor. A clean cloth can remove any remaining residue.

In Ottawa's climate, flame sensors often get dirty from dust accumulation during our long heating season. This is typically a $200-300 service call if you hire a technician, but it's one of the few furnace maintenance tasks homeowners can safely perform themselves. However, if you're uncomfortable working around gas appliances or notice other issues like unusual sounds or smells, it's best to call a licensed HVAC technician.

After cleaning and reinstalling the sensor, turn the gas back on and restore power to test your furnace. If the problem persists after cleaning, the sensor may need replacement or there could be other ignition system issues requiring professional diagnosis. Remember that only TSSA-licensed technicians should perform repairs on gas-burning components beyond basic maintenance like this.

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